Fujitsu ASU18RLF Service Instructions Manual page 30

Trouble shooting 7
INDOOR UNIT Error Method:
Indoor Heat Ex. Thermistor Error
Detective Actuators:
Indoor Unit Controller PCB
Heat Exchanger (MID) Thermistor
Forecast of Cause : 1. Connector failure connection 2. Thermistor failure 3. Controller PCB failuer
Check Point 1 : Check connection of Connector
Check if connector is loose or removed
Check erroneous connection
Check if thermistor cable is open
>>Reset Power when reinstalling due to removed connector or incorrect wiring.
OK
Check Point 2 : Remove connector and check Thermistor resistance value
Thermistor Characteristics (Rough value)
Temperature (°C )
Temperature (°F )
Resistance value (k )
Temperature (°C )
Temperature (°F )
Resistance value (k )
If Thermistor is either open or shorted, replace it and reset the power.
OK
Check Point 3 : Check voltage of Controller PCB (DC5.0V)
Make sure circuit diagram of each indoor unit and check terminal voltage at Thermistor (DC5.0V)
RED
1 1
1
CN3
2 2
2
WHITE
3 3
BLACK
1
CN1
BLACK
2
If the voltage does not appear, replace Controller PCB and execute the check operation again.
Indicate or Display:
Refer to error code table.
Detective details:
Indoor unit thermistor is open or short is detected always.
0 5 10
32 41 50
176 134 103
40 45 50
104 113 122
25.6 20.8 17.1
H/E Thermistor
BLACK
BLACK
Room Temp. Thermistor
15 20 25
59 68 77
80.3 62.9 49.7
02-09
30 35
86 95
39.6 31.7
DC